1. Field of the Invention
This invention is related to self-powered electric carts and in particular to an electrically powered push-type collapsible tricycle cart having dual independent motor drive.
Electrically powered vehicles are quite popular on golf courses. However, vehicles large enough for transporting passengers are generally expensive and therefore beyond the means of the average golfer to purchase or to transport to and from the golf course. On the other hand, light pull- or push-type golf carts are known for caddying golf bags alone. Such non-powered carts are quite popular, especially if collapsible. However, a non-powered cart becomes a major burden to drag or push around the golf course.
As a compromise, powered golf bag carrying carts have ben proposed. However, such powered carts have not met with success for various reasons. A number of such problems, prior proposed solutions and shortcomings of these solutions are illustrated by the prior art.
2. Description of the Prior Art
One example of a powered golf club carrying cart is described in U.S. Pat. No. 3,704,758 to Cropp, wherein a pair of d.c. motors is series connected to a large bank of rather heavy multi-celled batteries. Such a device is costly, excessively heavy, bulky, unsightly and not easily stored or transported and therefore not readily accepted by the average golfer. A relatively light, collapsible golf cart is therefore needed.
One proposed collapsible golf cart is described in U.S. Pat. No. 3,867,993 to Iizuka. The Iizuka patent describes a particular mechanism rendering a powered two-wheel cart collapsible. It has been found, however, that certain mechanisms of the Iizuka cart are subject to failure and frequent breakdown. For example, the legs of the Iizuka cart are subject to buckling and warping, and an internal main column slide bracket for supporting the legs is subject to jamming or sticking.
Two-wheeled carts are often found to be unsuited to power drive. Such carts with the power source (the battery) located along the main column may be easily upset if tipped too far. Prior three-wheeled arrangements, such as suggested in the Cropp patent may provide stability, but known arrangements are not suited to collapsible carts, where compact storability is a prerequisite.
It is often desirable to change the configuration of the collapsible carts slightly to accommodate the tastes of the operator or the terrain. For example, the operator may wish to raise or lower the steering arm, or it may be necessary to narrow the wheel base of the cart in order to negotiate a narrow path. It is thus desirable to include provision for adjusting steering arm height and for changing the drive wheel base without jeopardizing the performance of the cart. This might be done, for example, by assuring that the drive wheels remain parallel and vertical to the ground in cart configurations intermediate between fully collapsed and fully extended.
Providing continuously variable power to the drive motors presents special problems. Conventional d.c. power varying schemes such as bleeding excess drive current into a load resistance is wasteful of precious battery power. Alternating current control schemes are impractical in golf carts, since a.c. power is not readily available within practical weight and space constraints imposed by the need to provide a portable power source. In particular, known throttle transducer schemes, as suggested in the Cropp patent, or by Voight in U.S. Pat. No. 2,706,008, generally provide only discrete voltage levels of power through a tap changing switch.
A motorcycle type continuously variable throttle which might be located within a handle of a golf cart is subject to peculiar strains and shocks, particularly where the handle is also used to guide and control the golf cart. These factors must be taken into account in the embodiment of a practical throttle transducer.
The battery power sources for golf carts contain corrosive battery acid which, if accidently leaked or spilled, can cause considerable damage. Yet, practical batteries must be vented in order to prevent the equally dangerous build up of gases. Golf cart power packs also can be accidently tipped during transportation or storage. Thus, there exists a need to provide a vented battery which includes means for containing battery acid against spillage as might be caused by accidental tipping.
A major problem associated with powered golf carts is related to the differential action of the wheels and protection of the motors against shock caused by irregular terrain. Several solutions are known. One is described in U.S. Pat. No. 3,893,532 to Perlowin. Therein a belt drive is provided as a safeguard against terrain-caused shocks against the wheels which might damage the motor or the gearing.
Direct drive of the wheels is preferred, since energy transfer is much more efficient. Known direct drive schemes, however, suffer from the dual disadvantages of poor shock isolation and difficulties in turning. A powered golf cart can be turned in two modes. In one known direct drive scheme, one of the drive wheels may be speeded up relative to the nominal speed. This is suggested in the cart described in the Iizuka patent supra. Therein the cart includes individual wheel motors equipped with one-way clutches (the motors being coupled in parallel) which permits the wheels to travel at differing speeds while negotiating turns. This scheme has a number of disadvantages. First, the wheel on the inner turning radius will continue to rotate at the pre-turn speed. As a result the wheel on the outer turning radius must be accelerated to a velocity allowing the vehicle to turn. Second, in downhill travel, the wheels turn freely, since the motors provide no inertial resistance. As a consequence, the operator must provide all restraining forces on the massive load of cart, clubs and battery. And finally, the clutches employed therein are notoriously fragile and are prone to breakdown under terrain-induced shock.
In a further known direct drive scheme one of the wheels may be slowed down. A cart with two d.c. electric motors coupled to parallel and provided with a constant voltage tends to move in a straight line. An attempted turn causes substantial loading on one or other of the motors. The slower, more heavily loaded motor develops substantially higher torque than the faster motor and draws considerably higher current, resisting any attempt to turn the cart.
Series-connected d.c. motors, on the other hand, tend to transfer maximum drive power to the motor under the least load. As a result, turning is relatively easy. However, there are a number of drawbacks. For example, unequal loading between the wheels, as might be caused by misalignment of the wheels, travel along a hillside or travel over wet, loose or rocky terrain, causes power to be shifted to the least loaded motor. This may pull the cart to one side or cause wheels to spin earatically.
Thus, if the advantages of direct drive are to be obtained, then the differential problem and the shock isolation problem must be overcome.